Conventionally, a polyimide resin excellent in all of heat resistance, electric properties and mechanical properties is used for an insulating material of an electronic component and for a passivation film, a surface protective film, an interlayer insulating film, etc. in a semiconductor device. Among polyimide resins, those supplied in the form of a photosensitive polyimide precursor composition can easily form a heat-resistant relief-patterned coating film by applying the composition and subjecting the coating to exposure, development and thermal imidization treatment by curing. Such a photosensitive polyimide precursor composition is characterized by enabling a great reduction in processing time, compared with conventional non-photosensitive polyimide materials.
Meanwhile, a semiconductor device (hereinafter, sometimes referred to as “device”) is mounted on a printed circuit board by various methods according to the purpose. A conventional device is generally manufactured by the wire bonding method of connecting an external terminal (pad) and a lead frame of the device by a thin wire. However, in these days, with the increase in operation speed of the device and the rise of operation frequency to GHz, the difference in the wiring length of respective terminals in mounting comes to affect the operation of the device. Accordingly, mounting of a device for high-end applications requires accurate control of the mounting/wiring length, but it is difficult to satisfy this requirement by wire bonding.
To satisfy the requirement, flip-chip mounting where after forming a rewiring layer on a surface of a semiconductor chip and forming a bump (electrode) thereon, the chip is turned over (flipped) and directly mounted on a printed circuit board, has been proposed (see, for example, Patent Document 1). In this flip-chip mounting, the wiring distance can be accurately controlled. Accordingly, the flip-chip mounting is employed in a device for high-end applications dealing with a high-speed signal or because of a small mounting size, employed in a cellular phone, etc., and demands thereof are rapidly expanding. In the case of using a polyimide material for flip-chip mounting, it passes through a step of forming a metal wiring layer after a pattern is formed in the polyimide layer. The metal wiring layer is usually formed as follows. First, the polyimide layer surface is plasma-etched to roughen the surface, and a metal layer working out to a plating seed layer is formed to a thickness of 1 μm or less by sputtering. Thereafter, electrolytic plating is performed using the metal layer as an electrode to form a metal wiring layer. At this time, in general, Ti is used as the metal working out to the seed layer, and Cu is used as the metal of a rewiring layer formed by electrolytic plating.
With respect to such a metal rewiring layer, the adhesion between the rewiring metal layer and the polyimide layer must be high after a reliability test. The reliability test as performed herein includes, for example, a high-temperature storage test of holding the layers in an air with a humidity of 5% for 168 hours under the condition of 150° C.